Expanding shed roof.

Hi all,
I have a 24x12 shed/mini barn constructed of 2x4's (walls, rafters). I would like to expand the footprint of the shed to 24x16. To do so I am planning on building a 16 ft wide floor (did I mention that the shed doesn't have a floor?) under the shed, and extending the back part of the roof at the its current pitch (1/2) to meet an approximately 5ft tall wall at the 16 foot mark. So the new building would have a front roof span of 6.5 feet, and back roof span of approximately 11.5 feet.
I am considering either leaving a beam where the current back wall is (supported at 8' intervals) and just adding the additional approx 5ft roof made from 2x4s attached to this beam. This would be easiest and wouldn't change the shed much structurally (since it has mostly doors on the back anyway) but would leave pesky posts w/in the building. Another approach would be to sister the current 2x4 rafters (which are currently about 6.5 feet long) with 2x6's to span the 11ft (span tables show that they can handle it). But how to do this - is it okay to simply nail these larger rafters to the existing 2x4s and forget about it, or do I need to add additional cross bracing from the 2x6's to the front part of the roof (i.e. re-inforce the horizontal member which connects the rafters from the front and back parts of the roof, the name of which I can't remeber). Also would it be necessary/ recommended to beef up the front part of the roof? Or is there a better way?
Any and all input is welcome. Thanks in advance for your input. don
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On Mar 9, 8:30 am, snipped-for-privacy@gmail.com wrote:

really could use a picture
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than I am, marson.
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